Title page for ETD etd-38431826109623300


Type of Document Master's Thesis
Author Escobar, Jose Alejandro
URN etd-38431826109623300
Title Stress and fatigue analysis of svi-tested camshaft lobes
Degree Master of Science
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Kampe, Stephen L.
Landgraf, Ronald W.
Reynolds, William T. Jr.
Hendricks, Robert W. Committee Chair
Keywords
  • fracture surfaces
  • fatigue engine testing
  • rolling contact stress
  • fatigue life prediction
  • grinding residual stress
  • camshaft lobes
  • thermal damage
Date of Defense 1996-11-08
Availability unrestricted
Abstract
Nondestructive evaluation techniques were

employed to fully characterize three 2.3L

camshafts tested in an engine simulator for an

equivalent of 100,000 miles. Optical

microscopy, acoustic microscopy (SAM),

and profilometry were used to characterize

wear and fatigue, crack depth, and surface

roughness, respectively. Results show

cracking to occur mainly in the opening ramp

of the most abusively ground cam lobes. No

clear evidence was found for subsurface

cracking at depths as great as 200 mm from

the lobe's surface. Profilometry results show

no evidence of any major tribological effect

due to the sliding friction of the follower.

Fractography studies show a difference

between fracture surfaces among the cracks

examined; straight cracks exhibit features

resembling fatigue propagation, while fracture

surfaces from pitted cracks show a more

brittle behavior. Small grinding cracks

(approximately 300 mm in length) were found

in the opening ramps of the most abusively

ground lobes prior to testing. Knoop and

Nanoindenter microhardness indicate a

near-surface rehardening for the most

abusively ground lobe (confirmed by

metallography), and temper burn for the

remaining lobes. X-ray residual stress results

made in the opening ramp of the tested lobes

show evidence of residual stress relaxation.

X-ray line width data as a function of depth

does not correlate with residual stress.

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